A relational database can include a collection of relations, frequently known as tables. A table in the relational database can include a set of data elements or values that are organized using vertical columns and horizontal rows. The table can have a specified number of columns and a variable number of rows. Each column can have a data type that defines what category of data can be stored in the column. A row of a table can include one or more data fields. Each data field can correspond to a column, and have a data type that corresponds to the data type of the column. The type of a data column can be defined by a database schema, which can be a data model that defines how data in the relational database are represented or accessed.
Data in various tables of a relational database can be related in a database join operation. A join operation can combine data fields from two tables by using values common to each of the two tables. A database join can require a condition, also known as a join predicate. A result of the database join can include data from the two tables as well as results of various operations (e.g., mathematical operations, logical operations, or string operations) between various data fields of the tables.